全文获取类型
收费全文 | 37317篇 |
免费 | 6817篇 |
国内免费 | 7722篇 |
专业分类
测绘学 | 3729篇 |
大气科学 | 4636篇 |
地球物理 | 7558篇 |
地质学 | 20079篇 |
海洋学 | 4010篇 |
天文学 | 3391篇 |
综合类 | 2537篇 |
自然地理 | 5916篇 |
出版年
2024年 | 167篇 |
2023年 | 450篇 |
2022年 | 1233篇 |
2021年 | 1440篇 |
2020年 | 1369篇 |
2019年 | 1785篇 |
2018年 | 1243篇 |
2017年 | 1488篇 |
2016年 | 1498篇 |
2015年 | 1689篇 |
2014年 | 2139篇 |
2013年 | 2090篇 |
2012年 | 2235篇 |
2011年 | 2368篇 |
2010年 | 2001篇 |
2009年 | 2551篇 |
2008年 | 2493篇 |
2007年 | 2596篇 |
2006年 | 2508篇 |
2005年 | 2380篇 |
2004年 | 2109篇 |
2003年 | 1995篇 |
2002年 | 1717篇 |
2001年 | 1509篇 |
2000年 | 1515篇 |
1999年 | 1351篇 |
1998年 | 1168篇 |
1997年 | 861篇 |
1996年 | 728篇 |
1995年 | 607篇 |
1994年 | 562篇 |
1993年 | 498篇 |
1992年 | 354篇 |
1991年 | 311篇 |
1990年 | 214篇 |
1989年 | 165篇 |
1988年 | 145篇 |
1987年 | 87篇 |
1986年 | 54篇 |
1985年 | 36篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1954年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
181.
Magnetotelluric investigations have been carried out in the Garhwal Himalayan corridor to delineate the electrical structure
of the crust along a profile extending from Indo-Gangetic Plain to Higher Himalayan region in Uttarakhand, India. The profile
passing through major Himalayan thrusts: Himalayan Frontal Thrust (HFF), Main Boundary Thrust (MBT) and Main Central Thrust
(MCT), is nearly perpendicular to the regional geological strike. Data processing and impedance analysis indicate that out
of 44 stations MT data recorded, only 27 stations data show in general, the validity of 2D assumption. The average geoelectric
strike, N70°W, was estimated for the profile using tensor decomposition. 2D smooth geoelectrical model has been presented,
which provides the electrical image of the shallow and deeper crustal structure. The major features of the model are (i) a low resistivity (<50Ωm), shallow feature interpreted as sediments of Siwalik and Indo-Gangetic Plain, (ii) highly resistive (> 1000Ωm) zone below the sediments at a depth of 6 km, interpreted as the top surface of the Indian plate,
(iii) a low resistivity (< 10Ωm) below the depth of 6 km near MCT zone coincides with the intense micro-seismic activity in the
region. The zone is interpreted as the partial melting or fluid phase at mid crustal depth. Sensitivity test indicates that
the major features of the geoelectrical model are relevant and desired by the MT data. 相似文献
182.
The summer monsoon season of the year 2006 was highlighted by an unprecedented number of monsoon lows over the central and
the western parts of India, particularly giving widespread rainfall over Gujarat and Rajasthan. Ahmedabad had received 540.2mm
of rainfall in the month of August 2006 against the climatological mean of 219.8mm. The two spells of very heavy rainfall
of 108.4mm and 97.7mm were recorded on 8 and 12 August 2006 respectively. Due to meteorological complexities involved in replicating
the rainfall occurrences over a region, the Weather Research and Forecast (WRF-ARW version) modeling system with two different
cumulus schemes in a nested configuration is chosen for simulating these events. The spatial distributions of large-scale
circulation and moisture fields have been simulated reasonably well in this model, though there are some spatial biases in
the simulated rainfall pattern. The rainfall amount over Ahmedabad has been underestimated by both the cumulus parameterization
schemes. The quantitative validation of the simulated rainfall is done by calculating the categorical skill scores like frequency
bias, threat scores (TS) and equitable threat scores (ETS). In this case the KF scheme has outperformed the GD scheme for
the low precipitation threshold. 相似文献
183.
K. K. Singh R. P. Patel J. Singh B. Kumar A. K. Singh R. P. Singh B. L. Koul Lalmani 《Journal of Earth System Science》2008,117(3):219-225
In this paper, we report observations of unusual whistlers recorded at Jammu (geomag. lat. = 22°26′N; L = 1.17), India on March 8, 1999 during the daytime. They are interpreted as one-hop ducted whistlers having propagated along
higher L-values in closely spaced narrow ducts from the opposite hemispheres. After leakage from the duct, the waves might have propagated
in the earth-ionosphere waveguide towards the equator in surface mode. Tentative explanation of the dynamic spectra of these
events is briefly presented. 相似文献
184.
185.
186.
187.
文章通过详细的野外地质调查和系统的岩石化学、稀土元素、微量元素及硅、氧同位素等研究,探讨了羊蹄子山-磨石山钛矿区无矿白色硅质岩和富钛硅质岩的成因及形成地质构造环境。研究结果表明,呈厚层状产出的无矿白色硅质岩具较高的SiO2、Al2O3含量及Al/(Al Fe Mn)、Al2O3/(Al2O3 Fe2O3)比值,稀土元素总量很低,其北美页岩标准化配分模式为向右倾的曲线,无明显铈异常和铕异常,表明其形成于受陆源影响的大陆边缘构造环境;赋矿岩系中薄层状富钛硅质岩的TiO2、Fe2O3、Cu、V含量较高,但Al/(Al Fe Mn)、Al2O3/(Al2O3 Fe2O3)比值较低,稀土元素总量较高,北美页岩标准化曲线为明显左倾型-平坦型,具弱的负铈异常,表明其形成于洋脊及附近环境。两种硅质岩的δ30Si值为变化较小的负值,与热水沉积和某些生物成因硅质岩的硅同位素组成相似,两者的δ18O值范围和平均值均相似。两类硅质岩的成因及形成构造环境不同,富钛硅质岩的地球化学特征表明,该矿床的形成与本区元古宙海底火山热液喷流作用有关。 相似文献
188.
The Feiran–Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S1, and is almost everywhere parallel to lithological layering, S0. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S0. S1 formed by coaxial pure shear flattening strain (Z normal to S0, i.e. vertical; with X and Y both extensional and lying in S1). This strain also produced chocolate tablet boudinage of some layers and S1-concordant sills and veins. S1 has a strong stretching lineation L1 with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L1-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F1 folds with hinges parallel to the stretching lineation. F1 fold asymmetry variations do not support previous models involving macroscopic F1 folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran–Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia. 相似文献
189.
190.
广西大厂拉么锌铜多金属矿床成岩成矿作用年代学研究 总被引:20,自引:1,他引:19
本文对广西大厂矿田拉么矿区内出露的酸性侵入岩和矿石进行了精细的年代学研究,分别获得龙箱盖含斑黑云母花岗岩锆石原位SHRIMP UPb和全岩RbSr等时线年龄为94±4Ma(95%可信度)和98.6±1.9Ma(95%可信度),矽卡岩成矿期锌铜矿石中石英矿物RbSr等时线年龄为98.6±6Ma(95%可信度)。上述测定结果表明,拉么锌铜多金属矿床的成矿年龄与相关岩体的成岩年龄接近,均形成于早白垩世晚期。 相似文献